This invention relates to a pad wear indicating arrangement including a contact head embedded in the backing plate of a brakeshoe assembly and substantially flush with the surface of the backing plate remote from the friction pad, with the contact head having an electrical conductor enveloped by an insulating layer and extending from the backing plate on the side of the pad, and including further a socket connector adapted to be connected with the contact head and providing a connection between the electrical conductor and an indicating arrangement.
From German Published Patent Application DOS 1,959,983, a pad wear indicating arrangement is known which includes a contact head embedded in the backing plate of a brake-shoe assembly so it does not extend from the surface of the backing plate remote from the friction pad. The contact head is designed as a coaxial plug and includes a stud coaxially arranged in a sleeve. Stud and sleeve, which are both designed as electrical conductors, extend from the backing plate on the side of the pad. In the area facing the pad, the space between the stud and the sleeve is occupied by an insulating material. The part of the contact head remote from the side of the pad and not occupied by insulating material forms, owing to the sleeve and the stud, a coaxial plug. This part of the contact head which is designed as a coaxial plug is adapted to connect with a suitably designed socket connector from which a line leads to an indicating arrangement, thereby providing a connection between the electrical conductors of the contact head and the indicating arrangement.
From Brisish Pat. No. 1,445,539 another pad wear warning device is known which includes a contact head adapted to be plugged into a fastening sleeve rigidly secured to the backing plate and projecting from the side of the backing plate opposite the side thereof on which the pad is mounted. By means of radial projections at the contact head which are adapted to engage in recesses at the fastening sleeve, the contact head is held in the fastening sleeve in the manner of a bayonet catch. The contact head consists of an insulating body having a conductive loop arranged therein, with the contact head incorporating the conductive loop projecting away from the backing plate on the side close to the pad a preset degree. Electric wires that are connected to the conductive loop and rigidly secured to the contact head lead to a warning device. When the friction pad of the brake-shoe assembly is worn away, the brake disc will contact that part of the contact head that extends from the backing plate on the side close to the pad, thereby abrading the insulating layer until it contacts the conductive loop, abrading also this loop. As a result, the electrical connection to the warning device is interrupted which will provide an indication of the pad wear. However, in view of the fact that the contact head forms one structural unit together with the fastening elements, the conductive loop and the rigidly secured electric wires, the whole expensive unit has to be thrown away at each replacement of the brake-shoe assembly. There is also the risk that following replacement of the brake-shoe assembly, the replacement of the pad wear warning device is forgotten.
It is a further disadvantage in this pad wear warning device that the fastening sleeve projects a large distance away from the rear surface of the backing plate which presents an obstacle to a simple method of packaging and storing the brake-shoe assemblies since they do not allow stacking.